My earlier U.S. Pat. 5,085,667 describes stain-resistant nylon carpet made from cationic-dyeable carpet nylon which is dyed with an acid dye or premetalized acid dye. This carpeting is highly resistant to stains compared to previously available solution dyed nylon and acid dyeable (not modified with sulfonate containing compounds) nylon carpeting, particularly acid-type stains such as beverages containing FD & C No. 40 red and similar acid-based household stains. The disclosure of this patent is hereby incorporated by reference.
Although this product has excellent stain resistant properties I have now discovered and hereby disclose a manner to improve the resistance of this carpeting to household-type chlorine-based bleach products, typically laundry bleach based upon oxidative solutions of sodium hypochlorite, calcium hypochlorite, sodium hydrogen sulfite, chlorine water and hydrogen peroxide. Household bleaches are typically based upon sodium hypochlorite in aqueous solution and have a pH of about 10. These bleach products readily oxidize the dye in non-solution dyed nylon carpets and thus present a staining or color removal problem.
Prior proposals to protect fibers and articles from attack by bleaching solutions include providing a protective coating of a guanidine compound as described in published European application 0 297 748. Other proposals include imparting stain resistance to polyamide fibers and textiles by treating them with a fluorocarbon composition and subsequently a stain blocker as described in published European application 0 353 080.
Published European application 0 421 971 describes fibers prepared from a pigmented nylon polymer that has been modified to contain aromatic sulfonated units as an integral part of its polymer chain. Pigments are added to the polymer to impart color to the fibers prior to fiber extrusion as fibers made from the modified nylon polymer cannot be dyed with acid dyes by conventional techniques, according to this disclosure. The aromatic sulfonated units are incorporated into the polymer to improve the fiber's resistance to stains, acid dye food colorants, coffee and other food products. Pigmented yarns so prepared were heatset, tufted and tested for resistance to stains. Pigmented fibers of this type are limited to the producer-determined shades and cannot be dyed with acid dyes by conventional techniques. Resistance to acid-type stains derives from the presence of aromatic sulfonated units integrated in the nylon polymer chain and not by fiber processing or carpet-constructing procedures employed.
I have discovered and hereby disclose a more convenient and reliable process to achieve fiber and fabric protection and resistance to staining caused by aqueous solutions containing peroxygen groups, hypochlorite groups or mixtures of the two in which cationic-dyeable nylon fibers are dyed with an acid dye or premetalized acid dye at a pH of from about 4.0 to less than 7 in order to fix the dye into the fibers and, thereafter, subjecting the fibers to heatsetting for a period of time and at a temperature sufficient to impart the requisite degree of stain resistance to the nylon fibers.
Heatsetting closes the crystalline structure of the nylon fibers imparting further stain resistance. Specifically, heatsetting closes the fiber structure thus preventing or substantially reducing bleach access to the dye within the fiber protecting the dye from oxidation by the bleach. An open fiber structure allows bleach to enter the fiber and oxidize the dye contained in it. Heatsetting is accomplished using times and temperatures consistent with the physical properties and characteristics of the nylon fibers employed. It is important that the heating temperature stay below the softening/melting point of the nylon as established by the fiber producer's data specific to fiber type. As an illustration, for type 66 nylon the softening/melting temperature is in the 240.degree. C. to 255.degree. C. range and a range of 208.degree. C. to 212.degree. C. for type 6 nylon. Preferably a maximum heating temperature is chosen to be about 20.degree. C. below the softening/melting point of the fiber used. Heating times are selected to avoid fiber yellowing leading to change of shade, loss of fastness to light and reduced performance while the time the fibers are exposed to heat must be sufficient to close the fiber's crystalline structure. Heating times are related to heating temperatures and these two variables are selected such that during heatsetting operations the fiber reaches a temperature not exceeding its melting/softening point. Preferably heating times of about one minute, plus or minus 20 seconds at the temperature ranges noted above is sufficient to achieve bleach resistance while maintaining the other desired properties of fastness to light, resistance to acid-type stains, shade consistency and the like. Shorter times and lower temperatures reduce the effectiveness of the heatsetting treatment in closing the crystalline structure of the nylon fibers.
The nylon yarns are heat set under dry or very low moisture conditions in contrast to wet heatsetting procedures such as an autoclave or a Superba unit which use pressurized steam atmospheres. Dry air assures closing the fiber's crystalline structure while heatsetting in a moist environment opens the fiber's crystalline structure. Dry circulating air is preferred. Heated drums or rolls may be used but they tend to polish or partially remove crimp from the fibers.
Heatsetting is accomplished at temperatures in the range of about 160.degree. C. to about 220.degree. C. for a period of time of from about 40 seconds to about 80 seconds, generally about 1 minute. Type 66 cationic dyeable nylon is preferably heatset at temperatures in the range of about 195.degree. C. to about 220.degree. C. and for type 6 cationic dyeable nylon temperatures in the range of about 160.degree. C. to about 180.degree. C. Preferably the heatsetting is conducted in dry circulating air. Products so produced are tested for acceptance by soaking them in undiluted household bleach (Clorox.RTM.) solution and then assessing the change in color, if any, after a period of four hours.
Nylon carpet fiber is generally classified as to type, depending upon its receptivity to acid dyes and basic or cationic dyes. Cationic dyeable nylons contain SO.sub.3 H groups or COOH groups within the polymer structure in an amount sufficient to render the nylon fiber dyeable with a cationic dye which groups are receptive to cationic or basic dyes. Acid dyeable nylons are essentially conventional nylons, such as polyhexamethylene adipamide and polycaprolactam. Acid dyeable nylons vary as to type and are characterized as being weakly dyed with acid dyes, average dyed with acid dyes, or deeply dyed with acid dyes.
Cationic dyeable nylons generally exhibit inherent stain resistant properties, especially to acid-type stains, as compared to other nylon types used for carpet. Cationic dyeable nylons are dyeable with selected cationic dyes, but suffer from poorer lightfastness, especially in light shades, than do comparable shades dyed on acid dyeable nylon using monosulfonated or premetalized acid dyes. This has resulted in the the under-utilization of cationic-dyeable nylon as a carpet fiber. The fiber's inherently useful properties which otherwise make it attractive as a carpet fiber previously have not been fully realized.
This invention includes a procedure for dyeing cationic-dyeable nylon with acid and premetalized acid dyes resulting in nylon carpet having improved stain resistance and fastness properties.
The preferred techniques for practicing the invention include exhaust dyeing, pad/steam dyeing, continuous carpet dyeing and the like.
U.S. Pat. No. 5,085,667 provides an extensive list of acid dyes and premetalized acid dyes suitable for use in the present invention and a disclosure of this patent is hereby incorporated by reference.
U.S. Pat. No. 5,085,667 at column 10, lines 21-25 reported poor resistance of the product to bleach discoloration when compared with solution dyed nylon carpet. The procedures of the present application provide nylon carpet exhibiting resistance to bleach discoloration in a manner approaching that of solution dyed nylon carpet.
The procedures of the present invention serve to render the cationic-dyeable nylon resistant to bleaches with the heatsetting operation conducted at temperatures significantly higher than those used to exhaust dye the cationic-dyeable nylon alone. Compare exhaust dyeing temperatures as high as 212.degree. F. (100.degree. C.) to values nearly twice this amount using the heatsetting operation of the present invention. Moreover, the heatsetting operation is preferably conducted using dry or extremely low humidity circulating air.